Cu-doped Ag thin film, and preparation method and application thereof

Abstract

The application provides a Cu-doped Ag film and a preparation method and application thereof, and belongs to the technical field of electromagnetic protection materials. The Cu-doped Ag film provided by the application has a Cu doping concentration of less than or equal to 10 mol%, and the thickness of the Cu-doped Ag film is 5-20 nm. By doping copper in the silver film, the 3D growth of the silver film can be inhibited, and the planar growth of the silver film can be promoted, so that a uniform and continuous ultrathin silver film is formed. By controlling the thickness of the Cu-doped Ag film and the Cu doping concentration, the Cu-Ag film can simultaneously have high light transmittance and shielding effectiveness. The results of the examples show that the ultrathin transparent electromagnetic shielding film prepared by using the Cu-Ag film of the application has high light transmittance and shielding effectiveness, the visible light transmittance is higher than 79.2%, and the shielding effectiveness is higher than 36.8 dB in the range of 20 MHz to 5 GHz.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic protection materials, and in particular to a Cu-doped Ag film and a preparation method and application thereof. Background Art

[0002] With the widespread adoption of information technology equipment, particularly electromagnetic pulse weapons like ultra-wideband and high-power microwaves, the battlefield electromagnetic environment is becoming increasingly complex and harsh. Simultaneously, the increasing integration of information technology equipment is exacerbating the electromagnetic sensitivity and vulnerability of circuit systems. Consequently, electromagnetic protection for weaponry and equipment is becoming increasingly important. Many weapon systems, such as television-guided missiles, laser-guided missiles, and shielded cabins, require windows that combine high electromagnetic shielding performance with transparency.

[0003] Ultrathin metal films have attracted considerable attention in recent years due to their superior flexibility, high conductivity, unique optoelectronic properties, and remarkable stability compared to conventional conductive polymer-based film materials. Among them, silver has the highest electrical conductivity and the lowest optical loss. Therefore, high-quality ultrathin Ag films would be an ideal choice for transparent electromagnetic shielding windows. However, during the initial growth of Ag films, Ag atoms tend to bind to each other rather than to the substrate. When the film thickness is less than 20 nm, an "island effect" (i.e., Volmer-Weber growth mode) occurs. This effect leads to the formation of dispersed three-dimensional (3D) grains resembling "islands," making it difficult to form a continuous conductive Ag film. However, as the thickness of the Ag film increases, the isolated islands tend to merge to form a continuous conductive film, and optical transparency deteriorates.

[0004] Therefore, how to improve the preparation process of continuous ultra-thin Ag film so that it has excellent light transmittance and shielding effectiveness and is suitable for use as a transparent electromagnetic interference shielding window has become a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a Cu-doped Ag film and its preparation method and application. The Cu-doped Ag film provided by the present invention is uniform and continuous, and has both high light transmittance and shielding effectiveness, which is of great significance for the development of window materials with high light transmittance / high shielding effectiveness.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The invention provides a Cu-doped Ag film, wherein the Cu-doping concentration in the Cu-doped Ag film is less than or equal to 10 mol%, and the thickness of the Cu-doped Ag film is 5 to 20 nm.

[0008] Preferably, the Cu doping concentration in the Cu-doped Ag film is 1 to 8 mol %, and the thickness of the Cu-doped Ag film is 5 to 15 nm.

[0009] Preferably, the Cu doping concentration in the Cu-doped Ag film is 1 to 5 mol %, and the thickness of the Cu-doped Ag film is 7 to 12 nm.

[0010] The present invention provides a method for preparing a Cu-doped Ag thin film according to the above technical solution, comprising the following steps:

[0011] (1) performing hydrophilic treatment on the substrate to obtain a modified substrate;

[0012] (2) Using a silver target and a copper target as sputtering targets, a Cu-Ag film is prepared on the modified substrate obtained in step (1) by magnetron co-sputtering to obtain a Cu-doped Ag film.

[0013] Preferably, the substrate in step (1) is a SiO2 glass substrate.

[0014] Preferably, the hydrophilic treatment in step (1) comprises: ultrasonically treating the substrate with a hydrochloric acid solution.

[0015] Preferably, the volume ratio of the concentrated hydrochloric acid to deionized water is 1:(9-11).

[0016] Preferably, the vacuum degree of magnetron co-sputtering in step (2) is less than 10 -4 Pa, and the temperature of magnetron co-sputtering was room temperature.

[0017] Preferably, in the magnetron co-sputtering in step (2), the sputtering power of the silver target is 200-300W, and the sputtering power of the copper target is 80-240W.

[0018] The present invention provides the use of the Cu-doped Ag film described in the above technical solution or the Cu-doped Ag film prepared by the preparation method described in the above technical solution in electromagnetic shielding window materials.

[0019] The present invention provides a Cu-doped Ag film, wherein the Cu doping concentration in the Cu-doped Ag film is ≤10 mol%, and the thickness of the Cu-doped Ag film is 5 to 20 nm. By doping a certain concentration of copper into the silver film, the present invention can suppress the 3D growth mode of the silver film and promote the planar growth of the silver film, thereby forming a uniform and continuous ultra-thin silver film; by controlling the thickness of the Cu-doped Ag film and the Cu doping concentration, the Cu-Ag film can have both high light transmittance and shielding effectiveness. The results of the examples show that the ultra-thin transparent electromagnetic shielding film prepared from the Cu-doped Ag film provided by the present invention has both high light transmittance and shielding effectiveness, with a visible light transmittance of more than 79.2%, and a shielding effectiveness of more than 36.8 dB in the range of 20 MHz to 5 GHz, which is of great significance for the development of window materials with both high light transmittance and high shielding effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of magnetron co-sputtering according to the present invention;

[0021] Figure 2 SEM image of the Ag film provided for Comparative Example 1;

[0022] Figure 3 This is a SEM image of the Cu-doped Ag film provided in Example 1 of the present invention;

[0023] Figure 4 This is a SEM image of the Cu-doped Ag thin film provided in Example 2 of the present invention;

[0024] Figure 5 This is a SEM image of the Cu-doped Ag film provided in Example 3 of the present invention;

[0025] Figure 6 AFM images of the Cu-doped Ag thin films provided in Examples 1 to 3 of the present invention and the Ag thin film provided in Comparative Example 1;

[0026] Figure 7 XRD patterns of the Cu-doped Ag films prepared in Examples 1 to 3 and the Ag film provided in Comparative Example 1;

[0027] Figure 8 EDS analysis results of the Cu-Ag thin film (10 nm) with a copper doping concentration of 2 mol% prepared in Example 1;

[0028] Figure 9 This is the XPS spectrum of the Ag 3d peak of the Cu-doped Ag film prepared in Example 1 without Ar ion etching;

[0029] Figure 10This is the XPS spectrum of the Ag 3d peak of the Cu-doped Ag film prepared in Example 1 after Ar ion etching;

[0030] Figure 11 The transmittance of the Cu-doped Ag thin films prepared in Examples 1 to 3 and the Ag thin film provided in Comparative Example 1 in the wavelength range of 300 to 850 nm;

[0031] Figure 12 Shielding effectiveness of the Cu-doped Ag films prepared in Examples 1 to 3 and the Ag film provided in Comparative Example 1 in the frequency range of 20 MHz to 5 GHz;

[0032] Figure 13 Diagram of the shielding mechanism of Cu-Ag film;

[0033] Figure 14 This is a diagram showing the mechanism of the effect of copper doping on the shielding performance of silver thin films. DETAILED DESCRIPTION

[0034] The invention provides a Cu-doped Ag film, wherein the Cu-doping concentration in the Cu-doped Ag film is less than or equal to 10 mol%, and the thickness of the Cu-doped Ag film is 5 to 20 nm.

[0035] In the present invention, the Cu doping concentration in the Cu-doped Ag film is ≤10 mol%, preferably 1-8 mol%, more preferably 1-5 mol%, and even more preferably 2-5 mol%. By doping the silver film with a certain concentration of copper, the present invention can inhibit the 3D growth of the silver film and promote the planar growth of the silver film, thereby forming a uniform and continuous ultra-thin silver film. By controlling the copper doping concentration, the Cu-Ag film can have a high shielding effectiveness.

[0036] In the present invention, the thickness of the Cu-doped Ag film is 5 to 20 nm, preferably 5 to 15 nm, more preferably 7 to 12 nm, and even more preferably 10 nm. By controlling the thickness of the Cu-doped Ag film, the present invention avoids excessive thickness that results in poor optical transparency, thereby enabling the Cu-doped Ag film to simultaneously exhibit high light transmittance and shielding effectiveness.

[0037] The present invention suppresses the 3D growth mode of the silver film and promotes the planar growth of the silver film by doping a certain concentration of copper into the silver film, thereby forming a uniform and continuous ultra-thin silver film; by controlling the thickness of the Cu-doped Ag film and the Cu doping concentration, the Cu-Ag film can have both high light transmittance and shielding effectiveness, so that the prepared ultra-thin transparent electromagnetic shielding film has both high light transmittance and shielding effectiveness, with a visible light transmittance of more than 79.2% and a shielding effectiveness of more than 36.8dB in the range of 20MHz to 5GHz, which is of great significance for the development of window materials with both high light transmittance and high shielding effectiveness.

[0038] The present invention provides a method for preparing a Cu-doped Ag thin film according to the above technical solution, comprising the following steps:

[0039] (1) performing hydrophilic treatment on the substrate to obtain a modified substrate;

[0040] (2) Using a silver target and a copper target as sputtering targets, a Cu-Ag film is prepared on the modified substrate obtained in step (1) by magnetron co-sputtering to obtain a Cu-doped Ag film.

[0041] The present invention performs hydrophilic treatment on the substrate to obtain a modified substrate.

[0042] In the present invention, the substrate is preferably a SiO2 glass substrate. In the present invention, the light transmittance of the SiO2 glass substrate is preferably ≥ 92%. The present invention does not specifically limit the size and shape of the substrate, and can be determined based on the common knowledge of those skilled in the art. The SiO2 glass substrate used in the present invention has excellent light transmittance.

[0043] The present invention preferably cleans the substrate before the hydrophilic treatment. In the present invention, the cleaning method preferably includes: ultrasonically cleaning the substrate with a mixed solvent of ethanol and propanol, and then ultrasonically cleaning it with deionized water. In the present invention, the volume ratio of ethanol and propanol in the mixed solvent is preferably (4-5):1; the temperature at which the mixed solvent is ultrasonically cleaning the substrate is preferably room temperature; and the time for ultrasonically cleaning the substrate with the mixed solvent is preferably 2-2.5 hours. In the present invention, the time for ultrasonic cleaning with deionized water is preferably 2-2.5 hours. The present invention does not have any special restrictions on the power of the ultrasound during the ultrasonic cleaning, and conventional power settings can be used. The present invention can remove impurities on the surface of the substrate by cleaning the substrate, thereby laying the foundation for subsequent hydrophilic treatment.

[0044] In the present invention, the hydrophilic treatment method preferably includes: ultrasonically treating the substrate with a hydrochloric acid solution. In the present invention, the hydrochloric acid solution is preferably a mixture of concentrated hydrochloric acid and deionized water; the volume ratio of the concentrated hydrochloric acid to deionized water is preferably 1:(9-11), more preferably 1:10; and the concentration of the concentrated hydrochloric acid is preferably 12 mol / L. The present invention does not specifically limit the power of the ultrasonic treatment; conventional power settings can be used. The present invention increases the contact angle between the silver atoms and the substrate through hydrophilic treatment, thereby improving its wettability.

[0045] In the present invention, the temperature of the hydrophilic treatment is preferably 70-90°C, more preferably 75-80°C; the duration of the hydrophilic treatment is preferably 35-50 minutes, more preferably 40-45 minutes. By controlling the temperature of the hydrophilic treatment, the present invention can improve the treatment efficiency, thereby further improving the hydrophilicity of the substrate.

[0046] After the hydrophilic treatment is completed, the present invention preferably sequentially washes the hydrophilic treated product with deionized water and then dries it.

[0047] In the present invention, the deionized water cleaning time is preferably 2 to 2.5 hours; the deionized water cleaning method is preferably ultrasonic cleaning. The present invention does not specifically limit the power of the ultrasonic cleaning, and conventional power settings can be used. The present invention can remove residual hydrochloric acid through deionized cleaning.

[0048] In the present invention, the drying method is preferably drying in a freeze dryer. The present invention does not specifically limit the specific model or source of the freeze dryer; commercially available products familiar to those skilled in the art can be used. The present invention does not specifically limit the drying time; it only requires that residual moisture be completely removed. Drying in the present invention can prevent moisture from affecting subsequent magnetron sputtering.

[0049] After obtaining the modified substrate, the present invention uses a silver target and a copper target as sputtering targets, and prepares a Cu-Ag film on the modified substrate by magnetron co-sputtering to obtain a Cu-doped Ag film.

[0050] In the present invention, the purity of the silver target is preferably ≥99.9%; the purity of the copper target is preferably ≥99.9%. The sources of the silver and copper targets are not particularly limited and can be purchased commercially or prepared in-house. By controlling the purity of the silver and copper targets, the effects of impurities can be reduced.

[0051] Prior to magnetron co-sputtering, the present invention preferably performs single-target pre-sputtering to determine the relationship between the thickness of the silver and copper films and the sputtering time, and analyzes the sputtering rates of the silver and copper films at different magnetron co-sputtering powers. Through the above process, the present invention can determine the sputtering rates of the silver and copper targets at different magnetron co-sputtering powers, thereby facilitating control of the Cu doping concentration in the Ag film by adjusting the magnetron co-sputtering power.

[0052] In the present invention, the vacuum degree of the magnetron co-sputtering is preferably less than 10 -4 The present invention can reduce the influence of components in the air on the film by controlling the vacuum degree of magnetron co-sputtering, and further reduce the content of impurities in the film.

[0053] In the present invention, the ionized working gas for the magnetron co-sputtering is preferably argon with a purity of ≥99.9%; the flow rate of the ionized working gas is preferably 35 to 45 sccm, more preferably 40 sccm; and the working pressure of the magnetron co-sputtering is preferably 0.8 to 1.2 Pa, more preferably 1.0 Pa. By controlling the process parameters of the magnetron co-sputtering, the present invention can improve the efficiency of the magnetron co-sputtering and further reduce the impurity content.

[0054] In the present invention, the sputtering power of the silver target during magnetron co-sputtering is preferably 200-300 W, more preferably 250-300 W, and even more preferably 300 W; the sputtering power of the copper target is preferably 80-240 W, preferably 100-180 W, and even more preferably 120-150 W; and the magnetron co-sputtering time is preferably 5-15 seconds. By controlling the sputtering power of the silver and copper targets, the concentration of Cu doping in the Ag film can be adjusted, thereby regulating the properties of the film.

[0055] In the present invention, the distance between the silver target and the modified substrate and the distance between the copper target and the modified substrate during magnetron co-sputtering are preferably the same. In the present invention, the angle between the silver target and the modified substrate and the angle between the copper target and the modified substrate during magnetron co-sputtering are preferably the same. The present invention does not specifically limit the distances and angles between the silver target and the copper target and the modified substrate during magnetron co-sputtering, and these can be set according to the common technical knowledge of those skilled in the art.

[0056] The present invention provides the application of the Cu-doped Ag thin film described in the above technical solution in electromagnetic shielding window materials. In the present invention, the electromagnetic shielding window materials preferably include weapons and equipment, laser televisions, and laser-guided missiles.

[0057] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0058] Example 1

[0059] A Cu-doped Ag film, wherein the Cu-doped Ag film has a Cu doping concentration of 2 mol % and a thickness of 10 nm;

[0060] The method for preparing the Cu-doped Ag thin film comprises the following steps:

[0061] (1) First, a SiO2 glass substrate with a transmittance of ≥92% is ultrasonically cleaned for 2 h using a mixed solvent of anhydrous ethanol and propanol at room temperature, then ultrasonically cleaned for 2 h using deionized water, then the SiO2 glass substrate is hydrophilically treated, and finally the SiO2 glass substrate is cleaned with deionized water for 2 h, and dried in a freeze dryer to obtain a modified substrate; the volume ratio of anhydrous ethanol to propanol in the mixed solvent is 5:1; the hydrophilic treatment method is: ultrasonically treating the substrate with a hydrochloric acid solution; the hydrochloric acid solution is prepared by mixing concentrated hydrochloric acid and deionized water, the volume ratio of concentrated hydrochloric acid to deionized water is 1:10, and the concentration of the concentrated hydrochloric acid is 12 mol / L; the temperature of the hydrophilic treatment is 80°C, and the time of the hydrophilic treatment is 40 min;

[0062] (2) using a silver target with a purity of ≥99.9% and a copper target with a purity of ≥99.9% as sputtering targets, preparing a Cu-Ag film on the modified substrate obtained in step (1) by magnetron co-sputtering at room temperature to obtain a Cu-doped Ag film; the vacuum degree of the magnetron co-sputtering is <10 -4 Pa, the ionized working gas for magnetron co-sputtering is argon with a purity of ≥99.9%, and the flow rate of the ionized working gas is 40 sccm; the working pressure of the magnetron co-sputtering is 1.0 Pa; during the magnetron co-sputtering, the sputtering power of the silver target is 300 W, the sputtering power of the copper target is 80 W, and the magnetron co-sputtering time is 10 s.

[0063] Example 2

[0064] A Cu-doped Ag film, wherein the Cu-doping concentration in the Cu-doped Ag film is 5 mol %, and the thickness of the Cu-doped Ag film is 10 nm;

[0065] In the method for preparing the Cu-doped Ag thin film, the sputtering power of the copper target during magnetron co-sputtering is 160 W, and other conditions are the same as those in Example 1.

[0066] Example 3

[0067] A Cu-doped Ag film, wherein the Cu-doped Ag film has a Cu doping concentration of 10 mol % and a thickness of 10 nm;

[0068] In the method for preparing the Cu-doped Ag thin film, the sputtering power of the copper target during magnetron co-sputtering is 240 W, and other conditions are the same as those in Example 1.

[0069] Example 4

[0070] A Cu-doped Ag film, wherein the Cu-doped Ag film has a Cu doping concentration of 2 mol % and a thickness of 5 nm;

[0071] The method for preparing the Cu-doped Ag thin film comprises the following steps:

[0072] (1) First, a SiO2 glass substrate with a transmittance of ≥92% is ultrasonically cleaned for 1 hour using a mixed solvent of anhydrous ethanol and propanol at room temperature, and then ultrasonically cleaned with deionized water for 2 hours, followed by hydrophilic treatment of the SiO2 glass substrate, and finally the SiO2 glass substrate is cleaned with deionized water for 2.5 hours, and dried in a freeze dryer to obtain a modified substrate; the volume ratio of anhydrous ethanol to propanol in the mixed solvent is 5:1; the hydrophilic treatment method is: ultrasonically treating the substrate with a hydrochloric acid solution; the hydrochloric acid solution is prepared by mixing concentrated hydrochloric acid and deionized water, the volume ratio of concentrated hydrochloric acid to deionized water is 1:9, and the concentration of the concentrated hydrochloric acid is 12 mol / L; the temperature of the hydrophilic treatment is 90°C, and the time of the hydrophilic treatment is 45 minutes;

[0073] (2) Using a silver target with a purity of ≥99.9% and a copper target with a purity of ≥99.9% as sputtering targets, a Cu-Ag film is prepared on the modified substrate obtained in the step (1) by magnetron co-sputtering at room temperature to obtain a Cu-doped Ag thin film; the vacuum degree of the magnetron co-sputtering is <10-4Pa, the ionized working gas of the magnetron co-sputtering is argon with a purity of ≥99.9%, and the flow rate of the ionized working gas is 45sccm; the working pressure of the magnetron co-sputtering is 1.2Pa; the sputtering power of the silver target during the magnetron co-sputtering is 300W, the sputtering power of the copper target is 80W, and the magnetron co-sputtering time is 5s.

[0074] Example 5

[0075] A Cu-doped Ag film, wherein the Cu-doped Ag film has a Cu doping concentration of 5 mol % and a thickness of 5 nm;

[0076] In the method for preparing the Cu-doped Ag thin film, the sputtering power of the copper target during magnetron co-sputtering is 160 W, and other conditions are the same as those in Example 4.

[0077] Example 6

[0078] A Cu-doped Ag film, wherein the Cu-doped Ag film has a Cu doping concentration of 10 mol % and a thickness of 5 nm;

[0079] In the method for preparing the Cu-doped Ag thin film, the sputtering power of the copper target during magnetron co-sputtering is 240 W, and other conditions are the same as those in Example 4.

[0080] Example 7

[0081] A Cu-doped Ag film, wherein the Cu-doped Ag film has a Cu doping concentration of 2 mol % and a thickness of 15 nm;

[0082] In the method for preparing the Cu-doped Ag thin film, the magnetron co-sputtering time is 15 s, and other conditions are the same as those in Example 1.

[0083] Example 8

[0084] A Cu-doped Ag film, wherein the Cu-doped Ag film has a Cu doping concentration of 5 mol % and a thickness of 15 nm;

[0085] In the method for preparing the Cu-doped Ag thin film, the sputtering power of the copper target during magnetron co-sputtering is 160 W, the magnetron co-sputtering time is 15 s, and other conditions are the same as those in Example 1.

[0086] Example 9

[0087] A Cu-doped Ag film, wherein the Cu-doped Ag film has a Cu doping concentration of 5 mol % and a thickness of 15 nm;

[0088] In the method for preparing the Cu-doped Ag thin film, the sputtering power of the copper target during magnetron co-sputtering is 240 W, the magnetron co-sputtering time is 15 s, and other conditions are the same as those in Example 1.

[0089] Comparative Example 1

[0090] Ag film, thickness of 10 nm;

[0091] The preparation method of the Ag thin film comprises the following steps:

[0092] (1) First, a SiO2 glass substrate with a transmittance of ≥92% is ultrasonically cleaned for 2 h using a mixed solvent of anhydrous ethanol and propanol at room temperature, then ultrasonically cleaned for 2 h using deionized water, then the SiO2 glass substrate is hydrophilically treated, and finally the SiO2 glass substrate is cleaned with deionized water for 2 h, and dried in a freeze dryer to obtain a modified substrate; the volume ratio of anhydrous ethanol to propanol in the mixed solvent is 5:1; the hydrophilic treatment method is: ultrasonically treating the substrate with a hydrochloric acid solution; the hydrochloric acid solution is prepared by mixing concentrated hydrochloric acid and deionized water, the volume ratio of concentrated hydrochloric acid to deionized water is 1:10, and the concentration of the concentrated hydrochloric acid is 12 mol / L; the temperature of the hydrophilic treatment is 80°C, and the time of the hydrophilic treatment is 40 min;

[0093] (2) Using a silver target with a purity of ≥99.9% as a sputtering target, a Ag thin film is prepared on the modified substrate obtained in step (1) by magnetron co-sputtering at room temperature; the vacuum degree of the magnetron co-sputtering is <10 -4 Pa, the ionized working gas for magnetron co-sputtering is argon with a purity of ≥99.9%, and the flow rate of the ionized working gas is 40 sccm; the working pressure of the magnetron co-sputtering is 1.0 Pa; the sputtering power of the silver target during the magnetron co-sputtering is 300 W, and the magnetron co-sputtering time is 10 s.

[0094] Comparative Example 2

[0095] Ag film, 5 nm thick;

[0096] The preparation method of the Ag thin film comprises the following steps:

[0097] (1) First, a SiO2 glass substrate with a transmittance of ≥92% is ultrasonically cleaned for 1 hour using a mixed solvent of anhydrous ethanol and propanol at room temperature, and then ultrasonically cleaned with deionized water for 2 hours, followed by hydrophilic treatment of the SiO2 glass substrate, and finally the SiO2 glass substrate is cleaned with deionized water for 2.5 hours, and dried in a freeze dryer to obtain a modified substrate; the volume ratio of anhydrous ethanol to propanol in the mixed solvent is 5:1; the hydrophilic treatment method is: ultrasonically treating the substrate with a hydrochloric acid solution; the hydrochloric acid solution is prepared by mixing concentrated hydrochloric acid and deionized water, the volume ratio of concentrated hydrochloric acid to deionized water is 1:9, and the concentration of the concentrated hydrochloric acid is 12 mol / L; the temperature of the hydrophilic treatment is 90°C, and the time of the hydrophilic treatment is 45 minutes;

[0098] (2) Using a silver target with a purity of ≥99.9% as a sputtering target, a Ag thin film is prepared on the modified substrate obtained in the step (1) by magnetron co-sputtering at room temperature; the vacuum degree of the magnetron co-sputtering is <10-4Pa, the ionized working gas of the magnetron co-sputtering is argon with a purity of ≥99.9%, and the flow rate of the ionized working gas is 45sccm; the working pressure of the magnetron co-sputtering is 1.2Pa; the sputtering power of the silver target during the magnetron co-sputtering is 300W, and the magnetron co-sputtering time is 5s.

[0099] Comparative Example 3

[0100] Ag film, thickness 15 nm;

[0101] In the method for preparing the Ag thin film, the magnetron co-sputtering time is 15 s, and other conditions are the same as those in Comparative Example 1.

[0102] Figure 1 Schematic diagram of the present invention when magnetron co-sputtering is performed. Figure 1 It can be seen that when magnetron co-sputtering is performed again, the distances between the silver target and the copper target and the substrate are the same, and the angles between the silver target and the copper target and the substrate are also the same.

[0103] The surface morphologies of the Ag thin film provided in Comparative Example 1 and the Cu-doped Ag thin films prepared in Examples 1 to 3 were observed using a scanning electron microscope (SEM, ZEISS Gemini 300). The results were as follows: Figures 2 to 5 ,in Figure 2 The surface morphology of the Ag film provided in Comparative Example 1 is as follows: Figure 3 The surface morphology of the Cu-doped Ag film provided in Example 1 is as follows: Figure 4 The surface morphology of the Cu-doped Ag film provided in Example 2 is as follows: Figure 5 The surface morphology of the Cu-doped Ag film provided in Example 3. Figure 2 It can be seen that when there is no Cu atom doping, the Ag atoms have poor adhesion, so it is difficult to grow on the substrate in a planar manner, resulting in the Ag particles tending to aggregate with each other and forming an island-like dispersed distribution structure; Figure 3 It can be seen that when doping 2 mol% Cu atoms, the coverage of Ag particles on the SiO2 substrate increases, so the surface morphology becomes dense and continuous. This may be because the bond energy of Ag-Cu bond (176 kJ / mol) is higher than that of Ag-Ag bond (162±2.9 kJ / mol), showing higher stability and shorter average diffusion distance of Cu atoms. Therefore, Cu atoms are more easily fixed on the substrate and promote the heterogeneous nucleation of Ag atoms. Figure 4It can be seen that when the Cu doping concentration is 5 mol%, the surface morphology of the film shows a similar change trend. Compared with the pure Ag film, the film is composed of dense and uniform particles. Figure 5 It can be seen that when the Cu doping concentration in the film is 10 mol%, the Cu-Ag film shows a trend of transition from uniform particles to large "grains" and the appearance of some porosity. This is probably due to the excessive Cu atoms entering the Ag lattice, causing lattice distortion and a significant increase in the surface energy of the Ag atoms. Therefore, the quality of the Ag film can be improved by controlling the Cu doping concentration.

[0104] The surface morphology of the Ag film provided in Comparative Example 1 and the Cu-doped Ag films prepared in Examples 1 to 3 were observed using an atomic force microscope (AFM, Bruker Dimension Icon) to obtain the roughness of the films, which was then converted into AFM. Figure 6 As shown. Figure 6 It can be seen that as the Cu concentration increases from 0 to 10 mol%, the RMS roughness of the film decreases significantly from 5.32 nm to 0.88 nm, then increases slightly to 0.95 nm, and finally increases to 2.13 nm. This indicates that slight Cu doping can significantly enhance the growth of 2D planes, resulting in a relatively smooth surface morphology of the film, which is consistent with the Figures 2 to 5 However, excessive Cu atoms can lead to lattice distortion, high surface energy, and grain agglomeration, resulting in a rough surface morphology.

[0105] The structural parameters of the Cu-doped Ag films prepared in Examples 1 to 3 and the Ag film provided in Comparative Example 1 were tested, and the results are shown in Table 1:

[0106] Table 1 Structural parameters of the Cu-doped Ag films prepared in Examples 1 to 3 and the Ag film provided in Comparative Example 1

[0107]

[0108] Figure 7 XRD patterns of the Cu-doped Ag films prepared in Examples 1 to 3 and the Ag film provided in Comparative Example 1. Figure 7 It can be seen that compared with the PDF 04-0783 card of Ag, all the detected peaks are accurately attributed to the characteristic peaks of the Ag lattice, among which the diffraction peak intensity of the (111) crystal plane is the highest. It can be inferred that the phase structure of the Cu-Ag film only contains the Ag phase, and the original Ag structure is not changed due to the doping of copper. The structural parameters of the Cu-doped Ag films prepared in Examples 1 to 3 and the Ag film provided in Comparative Example 1 were also tested, including the diffraction angle 2θ (111), full width at half maximum (FWHM) and average grain size, the results are shown in Table 1. Combined with the data in Table 1, the FWHM of the (111) peak is substituted into the Scherrer formula to estimate the crystallite size: D = kλ / (βcosθ), where k is the Scherrer constant (0.89), λ is the X-ray wavelength (0.15405nm), θ is the Bragg angle, and β is the FWHM value obtained using Jade 6.0 software. In addition, with the increase of Cu atoms, it can be observed that the characteristic peak (111) shifts to the right, which indicates that the interplanar spacing decreases, as shown in Figure 1. Figure 7 This phenomenon can be explained by the fact that some Cu atoms enter the Ag lattice. and The difference in atomic radius leads to lattice distortion.

[0109] According to the above studies, it can be seen that the film doped with 2 mol% Cu exhibits the most excellent surface morphology compared with films with other Cu concentrations. This indicates that 2 mol% Cu concentration is the best choice for preparing high-quality Ag films.

[0110] Figure 8 The EDS analysis results of the Cu-Ag thin film (10 nm) with a copper doping concentration of 2 mol% prepared in Example 1 are shown in FIG. Figure 8 It can be seen that the peaks corresponding to Cu and Ag elements are clearly visible in the spectrum (see Figure 8 a). In addition, the EDS spectrum shows that two atoms ( Figure 8 b and 8c) are relatively uniform, further confirming that the Cu-Ag film is uniform when the copper doping concentration is 2 mol%, which is consistent with Figure 3 The SEM results are in good agreement.

[0111] The chemical state and content of Ag element in the Cu-doped Ag film prepared in Example 1 were studied using an X-ray photoelectron spectrometer (XPS, Thermo ESCALAB 250XI), and the results were as follows: Figure 9 and Figure 10 ,in, Figure 9 This is the XPS spectrum of the Ag 3d peak without Ar ion etching. Figure 10 This is the XPS spectrum of the Ag 3d peak after Ar ion etching. Figure 9 and Figure 10 It can be seen that the unetched surface analysis shows that the Ag 3d 3 / 2 and 3D 5 / 2 The peak was identified as elemental Ag. In addition, a small peak was observed at 369.3 eV, indicating the presence of AgO ( Figure 9This may be because during the experiment and testing process, the surface Ag atoms inevitably reacted with the air to generate AgO. However, after Ar ion etching to a depth of 5nm, no additional peaks related to AgO were detected, and all Ag 3d peaks belonged to elemental Ag ( Figure 10 ). Through analysis, it can be inferred that the content of AgO is relatively small and exists almost only in the surface area. In fact, the conductivity of Ag and AgO is quite different, that is, the conductivity of elemental Ag is a good conductor, which is about 6×10 7 S / m, while AgO is an insulator with a conductivity of 10 -8 ~10 -10 Therefore, elemental Ag plays a dominant role in the conductivity of the film, rather than AgO, which has obvious benefits for its shielding effectiveness.

[0112] The transmittance of the Cu-doped Ag films prepared in Examples 1 to 3 and the Ag film provided in Comparative Example 1 in the wavelength range of 300 to 850 nm was measured using an ultraviolet-visible near-infrared spectrophotometer (UV-VIS spectrum-NIR, INESA752G). The results are as follows: Figure 11 As shown. Figure 11 It can be seen that the SiO2 glass substrate has a very high visible light transmittance, with an average transmittance of 93.5%, and is therefore more suitable as a substrate. The Ag film provided in Comparative Example 1 exhibits a wide surface plasmon resonance (SPR) behavior in the visible light region, which indicates that the grain size is uneven, which is consistent with the Figure 2 The SEM results in are consistent. However, with the increase of Cu atom doping amount, the SPR behavior of Cu-Ag film gradually weakens until it disappears. This is attributed to the fact that the introduction of Cu atoms into the lattice replaces some Ag atoms, resulting in large lattice distortion, vacancies and dislocations and other defects, which can destroy the orderly arrangement of the particle lattice. Therefore, electron scattering increases and the mean free path (EMFP) of molecules decreases, resulting in the attenuation and damping of surface plasma, further weakening the SPR behavior of Ag. At the same time, with the increase of Cu doping concentration, the average transmittance of Cu-Ag film in the visible light range gradually decreases. Among them, the transmittance of Cu-doped Ag film prepared in Example 1 is the highest, reaching 79.7% at around 400nm. This is because Cu doping greatly improves the uniformity and density of the Ag film and reduces the roughness. However, excessive Cu doping will introduce defects in the film. These defects can act as scattering centers, significantly increasing light scattering, which in turn reduces the transmittance of Cu-Ag film, resulting in a slight decrease in the transmittance of Cu-doped Ag film prepared in Examples 2 to 3.

[0113] The shielding effectiveness of the Cu-doped Ag films prepared in Examples 1 to 3 and the Ag film provided in Comparative Example 1 in the frequency range of 20 MHz to 5 GHz was measured by a vector network analyzer (Ceyear 6371D) using a coaxial method. The results are shown in FIG. Figure 12 As shown, the shielding mechanism of Cu-Ag film is as follows Figure 13 As shown in the figure, the effect of copper doping on the shielding performance of silver thin films is as follows Figure 14 As shown. Figure 12 It can be seen that the shielding effectiveness (SE) of pure Ag film is low, with an average value below 5 dB, which is due to its discontinuous surface morphology ( Figure 2 However, compared with pure Ag film, Cu doping can effectively improve the electromagnetic shielding capability of Ag film. When the Cu doping concentration is 2 mol% (ie, Example 1), the shielding effectiveness of Cu-Ag film is the most outstanding, with a peak value of up to 36.8 dB.

[0114] The SE of Ag film is studied using the analytical formula of electromagnetic shielding theory as follows:

[0115] SE=A+R+BI

[0116]

[0117]

[0118]

[0119] Where A is the absorption loss, B is the multiple reflection loss, and R is the reflection loss. t is the thickness of the film, f is the frequency of the electromagnetic wave in the range of 20MHz to 5GHz, μr is the relative magnetic permeability, which is 1, and σ r is the relative conductivity of the film, and γ is the propagation constant.

[0120] pass Figures 12-14 Analysis shows that absorption loss occurs when electromagnetic waves are incident on the surface of the film. Due to the nanometer thickness of the film, A calculated by formula II is about 0.1dB and can be ignored. At the same time, according to formula III, B is also very low, close to the order of A. According to formula I, the SE of the film mainly depends on R. By analyzing formulas I and IV, it can be seen that the SE characteristics of the film are mainly determined by σ r The value of σ r The value of varies with the quality of the film with different Cu doping concentrations. Obviously, the direct reason for the insufficient conductivity of pure Ag film is that there are cavities (similar to high-resistance resistors) between the Ag particles with 3D island distribution. Figure 14 a). In addition, it is also affected by the rough topography that induces electron scattering at the interface, surface and grain boundary. However, by doping Cu atoms in Ag thin films, e.g. Figure 14 As shown in (b), 3D Ag islands can be transformed into a continuous 2D Ag film due to Cu acting as a heterogeneous nucleation site for Ag atoms. Thus, a continuous conductive channel is formed in which charge carriers can flow freely through the ocean of electrons.

[0121] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a Cu-doped Ag thin film, comprising the following steps: (1) performing hydrophilic treatment on the substrate to obtain a modified substrate; (2) using a silver target and a copper target as sputtering targets, preparing a Cu-Ag film on the modified substrate obtained in step (1) by magnetron co-sputtering to obtain a Cu-doped Ag film; The substrate in step (1) is a SiO2 glass substrate; the hydrophilic treatment in step (1) includes: ultrasonically treating the substrate with a hydrochloric acid solution; the hydrochloric acid solution is prepared by mixing concentrated hydrochloric acid and deionized water; the concentration of the concentrated hydrochloric acid is 12 mol / L; and the volume ratio of the concentrated hydrochloric acid to the deionized water is 1:(9-11); In the step (2), the sputtering power of the silver target during magnetron co-sputtering is 200-300 W, and the sputtering power of the copper target is 80-180 W; The Cu doping concentration in the Cu doped Ag film is less than or equal to 10 mol %, and the thickness of the Cu doped Ag film is 5 to 20 nm.

2. The preparation method according to claim 1, characterized in that The vacuum degree of magnetron co-sputtering in step (2) is less than 10 -4 Pa, and the temperature of magnetron co-sputtering was room temperature.

3. The preparation method according to claim 1, characterized in that The Cu doping concentration in the Cu doped Ag film is 1-8 mol %, and the thickness of the Cu doped Ag film is 5-15 nm.

4. The preparation method according to claim 1, characterized in that The Cu doping concentration in the Cu doped Ag film is 1-5 mol %, and the thickness of the Cu doped Ag film is 7-12 nm.

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